1. Field of the invention
The present invention relates generally to automotive transmissions and more specifically to an improved control arrangement for a transmission system having a lock-up clutch associated with the torque converter of the system.
2. Description of the Prior Art
NISSAN AUTOMATIC TRANSAXLE SERVICE MANUAL - for the RE4R01A type transmission (published in March 1987) discloses in section I page 28 to 29 an example of a transmission system of the type wherein a lock-up clutch associated with the torque converter is controlled by an arrangement wherein a fully closed throttle condition is detected using the output of an idle switch. The output of this switch is used in combination with a vehicle speed indicative signal in a manner wherein, when the vehicle speed is above a predetermined level and the idle switch is OFF, a control solenoid is energized in a manner which induces lock-up clutch engagement and provides a positive drive connection between the engine (prime mover) and the transmission per se in all foward gears. When the vehicle speed is below the above mentioned level and the idle switch is ON, the control solenoid is de-energized and the lock-up clutch is released to permit torque multiplication by the torque converter.
However, this arrangement has suffered from the drawback that as the throttle valve is operatively connected with devices such as dashpots, choke controls and the like to prevent excessively rapid closure and/or keep the throttle valve opened by a predetermined amount, it sometimes occurs that even though the driver has released the accelerator pedal, the throttle valve does not synchronously assume a closed position in the throttle chamber. This leads to the situation wherein the idle switch does not close and indicate the change in demand, and prevents the lock-up control solenoid from being appropriately de-energized. This results in an undesirable shuddering phenomenon being produced particularly at high vehicle speeds wherein sudden vehicle deceleration is induced.